This invention relates to solving problems on developer rollers as used in Xerography and more specifically in the toner cartridge remanufacturing industry. This includes copiers, laser printers and facsimile machines.
CANON has designed an all-in-one cartridge as in U.S. Pat. No. 4,975,744, issued Dec. 4, 1990 and assigned to CANON. Several companies have used these cartridges in laser printers, copy machines and facsimile machines, each with the varying printer engines and a different nameplate. Originally, these cartridges were designed to be "disposable". However, after the first all-in-one toner cartridge was introduced, it did not take long before laser cartridge remanufacturers such as applicant began remanufacturing cartridges. These "disposable" cartridges were designed to function for only one cartridge cycle without remanufacturing. The remanufacturers had found certain components that needed replacement on a regular basis. In 1990, the first aftermarket photoreceptor drum became available for use in remanufacturing the all-in-one cartridge of the "SX" engine variety, the most popular printer cartridge from around 1987 through 1994 at the time of this writing. When the long-life photoreceptor drum became available, the entire remanufacturing industry turned around and gained great strength and began a huge growth surge that still continues. In October 1993, HEWLETT-PACKARD, the largest seller of this printer engine using the all-in-one cartridge, entered the cartridge remanufacturing industry with the "Optiva" cartridge, further increasing the size as well as credibility of this relatively new industry. However, this relatively new industry grew from the all-in-one cartridge shortly after its debut. Before the introduction of the long-life drum, sometimes called the "superdrum" or "duradrum", the SX cartridge would last for around three cartridge remanufacturing cycles at best, since the maximum useful life of the OEM drum was three cycles. However, the long-life drums got their names from the fact that they were designed to last for many remanufacturing cycles or recharges as they are sometimes called. Typically, the long life drum can last for ten or more such cycles, unlike the typical OEM (Original Equipment Manufacturer) drum. With the additional developments of drum coatings, originally designed for OEM drums, the long-life drum may last for many additional cycles. Some coatings, in theory, were designed to be dissolved and removed from over the drum surface every 1-3 cycles, so the drum life of the long-life drum almost seems limitless.
However, with photoreceptor drums lasting for many cycles, other components of the cartridge have a tendency to require greater durability, a better solution, or a greater life. Also, as the success of these cartridges has skyrocketed, the demand is for cartrides with longer cycles, so component improvements are significant. Therefore, avoiding natural problems with prevention means must also be implemented for cartridges of longer life both in longer cycle times and greater number of cycles. Developer rollers and related components are no exception. They do not last indefinitely although there are some things that may be done to increase the life expectancy.
First, the most often seen developer roller contact has been the OEM copper alloy helical spring to supply a bias voltage to the inside wall of the developer roller. Many developer rollers have a magnetic core. The rotating helical spring is in constant contact with a stationary stainless steel spring-loaded welded-washer subassembly, where the welded-washer is contiguous with the assembly where printer contact is made. As the developer roller rotates, the helical spring is always in contact with the stainless steel welded-washer subassembly. The welded-washer subassembly provides the helical spring with the bias voltage connection supplied by the printer's electronic circuitry which then supplies the bias voltage to the aluminum developer roller sleeve on the inner wall. However, on a random basis, more frequently than desired, this connection between the stainless steel washer and the helical spring loses its integrity. It wears. It loses its spring force. The spring may be bent back to its original "design" position, but, it is a fairly time consuming task to bend it back out and even more difficult to obtain the correct bend. The OEM helical spring connects to the inner wall of the developer roller aluminum sleeve by digging into the inner wall with 2-4 prongs that eventually loosen up and decrease the quality of the electrical connection. Both the spring and washer may obtain deposits of insulative toner, or oxidation from the spring copper of the helical spring. Even a speck of insulative debris is enough to ruin the integrity of this connection. Since it rotates, the connection must be thought of as a connection for 360 degrees of rotation. A little speck of discontinuity is all it takes to ruin what would have otherwise been a perfect image. Similarly, in a 360 degree rotation of the developer roller, a small amount of imperfection from out-of roundness may also cause a decrease in integrity of the connection between the helical spring and the welded-washer subassembly. With this system, there are many places where it can go wrong. For example, the location where the washer touches the source of the bias voltage. There is the connection where the helical spring rotates, touching the welded-washer subassembly. The helical spring is part of an assembly that fits inside the developer roller. The assembly "bites" into the inner wall (usually aluminum) of the developer roller. It may eventually lose good contact at that point. Typically, these developer roller contacts bite into the inner wall in two or three small places. It may lose its connection integrity from the spring losing its original resiliency. However, whatever the reason it loses its integrity, it does not function the same as brand new over many cycles. Furthermore, the replacement components are not available from the OEM manufacturer. Consequently, remanufacturers have had to come up with their own solutions to this problem. Many Americans livelihoods are at stake when you look at the size of the cartridge remanufacturing industry.
I introduced the first solution to the problem when I wrote an article over two years ago about using conductive grease in this assembly where the helical spring contacts the stainless steel washer (Recharger February 1992, pg 95, "Tech Talk and New Ideas"). Others soon copied this idea and used other conductive greases. In the Summer of 1993 the debate began about which conductive greases are appropriate. There are two schools of conductive greases, very generally. The first type function well in practice, but by themselves do not conduct current as measured with a voltmeter or ohmeter. However, although this produced "miracle" results with my customers, the effectiveness of the grease fell off near the end of the cartridge cycle when the grease was gone. Furthermore, to grease the helical spring area for every cartridge cycle is too labor intensive. After getting to the difficult to reach helical spring and stainless steel washer, reassembly of the developer roller is very time consuming. This was the first fix known for this problem. Among the symptoms of not fixing this problem are uneven darkness on the output page, uneven blacks, uneven gray shades, and unsolid blacks. By using the conductive grease, the problem goes away. However, it is cumbersome to apply. I have been searching for a better way.
The other conductive grease, used by some, is a black conductive grease. This grease, when measured with an ohmeter, has continuity at any distance. However, unlike the other described grease which wears away near the end of the cycle, the black grease cakes up or hardens before the end of the cartridge cycle. In conclusion, conductive greases were a good fix before other solutions came about.
Applicant has invented a conductive grease that is a combination of the two schools of thought. By mixing the conductive grease that measures no conductivity with conductive carbon black and/or graphite, a conductive grease has been developed that has properties of each type and is conductive when measured with an ohmeter. By using silicon grease, a nonconductive, insulating grease used in automotive and aircraft industry, used as an insulative material around battery terminals, ignition systems, and sparkplug connections, to prevent corrosion, a material is made by DOW CORNING Corporation that meets the MIL-S-8660 specification and is essentially a moisture barrier. Any such insulative silicone grease, like the kind you see in an automotive store may be used as the main ingredient. By mixing the insulative grease with either/or conductive carbon black and/or conductive graphite, a highly conductive yet moisture-free conductive grease was developed for use where electrical connections are made and particularly electrical connections where there is mechanical motion. The conductive grease maintains the conductivity throughout at the contact points and is particularly useful in the imaging industry for charge roller contacts, drum axle contacts, and particularly developer roller bias contacts, as they will be discussed throughout this application.
A second improvement involves a spring inside the developer roller. In this development remanufacturers began by removing the helical spring assembly from inside the developer roller. They snipped off the helical portion, two helical prongs, from the helical spring assembly, placed the modified helical assembly back in the developer roller tube (no longer helical), and placed a coil spring between the assembly and the stainless welded-washer subassembly. I used a steel piano wire coil-spring in this place. One company used a copper alloy coil spring. Another company replaced the spring assembly with a copper alloy assembly to receive the coil spring and added to it a copper alloy washer to replace the stainless steel washer which may be used as an addition to it and the coil spring. However, this product was practical for large customers for only one main reason. It was found that reliability was low until the user used the product for a while. Then cartridge technicians began using assembly jigs to accurately place either the original modified helical assembly or its replacement assembly into the developer roller. Since precision is important, some remanufacturers find this kind of product desirable and others find it too time consuming. Many do not have the patience to learn to use it correctly. Even so, coil springs lose resilience with wear-time and this product, even when properly installed, has a limited life.
Another product that has come on the market is a clip for providing the bias voltage directly from the doctor blade to the developer roller, similar to the spring. The clip, similarly helps the bias voltage stay in contact with the developer roller sleeve, but on the outside wall of the developer roller sleeve, but it cuts a groove in the outer wall. The bias voltage is important for transporting toner from the developer roller to the photoreceptor drum. It is transported by two main forces. First, the photoreceptor drum has a charge on it for white space and a lack of or lesser charge where there is black image space. In other words, the charged surface of the photoreceptor drum repels toner while the uncharged pixels, where charge was removed by laser light, attract toner from the surface of the developer roller. The developer roller is continually ready to move toner to and from the photoreceptor drum in this selective fashion. However, the developer roller has a bias voltage that essentially in simplification repels and attracts toner to and from the photoreceptor drum. It is this bias voltage that is at the very core of the main problems that are solved in this invention. In simple terms, the bias voltage has an AC and DC component. The AC component essentially charges typically at 1600V AC and 1800 HZ while the DC component charges typically at -500 volts DC. The AC component at 1800 HZ essentially causes toner to jump on and off the developer roller sleeve, thus supplying a cloud of toner to the photoreceptor.
It is the continuity of the bias voltage that is the heart of the described prior art as well as an embodiment of this invention. For example, the conductive grease helped prevent the bias voltage discontinuity. The coil spring and kits, as well as the clip, did the same. However, a simpler, more effective bias voltage connector is needed.
The concept of static elimination/limitation is a known concept in electrostatics. For example, any sharp pointed metallic object that is either grounded or oppositely charged than an existing electrostatic charge or source of such a charge will diminish that charge. A static limiter device, however, consists of a set of many such pointed grounded or oppositely charged points. Some use sharp pointed metal and others use a metal object with a set of several evenly spaced wires protruding. This type of a device has been used in the SX printer, for example, in prior art, for charging the paper negatively (rather than grounding) to prevent thin paper from wrapping around the negatively charged photoreceptor drum at the transfer station where a positively charged transfer corona assembly charges. This is located in the printer, not in the toner cartridge. A device is needed to control the static electricity in the toner cartridge assembly adjacent the developer roller and drum to maintain the quality of the image. This device would increase the integrity of the bias voltage for better contact and, therefore, better image consistency and quality while allowing the printers, copiers and facsimile machines to operate under conditions that in current state-of-the-art it could not. With such a device the machines would be able to operate in a wider humidity range, at high altitudes, in the dry seasons when outdoor weather is very cold (although the machine is indoors) and in dry desert climates.